I work in Delaware and live in PA. The law in Delaware is clear: My side programming projects are my property and not my employer's, unless I do something on the side that's very similar to the paid work. (See DE code chapter 19 section 805 here: http://codes.lp.findlaw.com/decode/19/8/805).

Nevertheless my employer doesn't want to provide me with a piece of paper recognizing my right to my own side projects or even the legitimacy of that DE statute.

Still they wanted a list of all my projects before I started, which is perhaps 20 total. Since then I've put out over 10 iOS apps that I wrote in the evenings.

You might want to be careful and find legal advice, and then you have to weigh-in the advice with the relationship you want to keep with your job. It is possible that denying this information will put you in the dog house (in which case you might not want to work there anyway). They've put you in a tough spot.

I don't discuss my side projects with my current employer, but I go to great lengths to make sure I don't spend work time on my side projects. If you've done that, that's an upside.

Late answer, but I think getting legal advice might be a good option. I'd be inclined to tell them to go away politely, if the professional advice says it is okay to do so. Whilst I understand legitimate concerns from employers about intellectual property, what you do in your own time is (mostly) none of your employer's business.
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halferNov 26 '11 at 15:16

Give them the info. If you are REALLY paranoid about it, have your attorney deliver the info to their attorney, Registered Mail, Return Receipt Requested, with appropriate lawyerese about how this is the disclosure that they requested and they are expected and required by law to respect your intellectual property blahblahblah.

You have now told them what you have previously done, and put them on notice that they can't claim this previous work as their own. You MAY limit your career options, as they MIGHT not want you working on something similar. Or you may WIDEN your career options, as they might not have known about this area, and it might be knowledge they really need (and want to pay for).

They are not free to ignore the law, a fact that your attorney and the justice system will be more than happy to explain to them, should it come to that. They cannot demand that you give them the stuff you did before you came on board.